Two Red Tail Sharks Chasing Each Other

I'm looking into red tail sharks and my friend has a pair who constantly chase each other. They never nip but is this playing or aggression? They're in a 50 gallon tank with some neon tetras. Wondering what the minimum gallon requirements are and if they're supposed to be so active. Thanks

Update: Gave one of the red tail sharks to my local aquarium store (goodbye Henry) and the one who stayed seems so much happier. Thanks for the feedback!